1. Field of Invention
This invention relates to vehicle rollover protection. In particular, the invention relates specifically to a roof geometry for increased rollover crush resistance and a structure for integration or retrofit in vehicles to provide an enhanced structural capability for the protective geometry.
2. Description of Prior Art
Rollovers have been and continue to be a significant cause of occupant fatalities and serious injuries. When a vehicle rolls over the laws of physics induce the roll about a longitudinal roll axis which passes through the center of mass of the vehicle. As the vehicle rolls, it touches down on each corner of the vehicle when viewed from the front as in FIGS. 1A and 1B. A vehicle like a sport utility vehicle (SUV) 2 shown in FIG. 1A and a passenger car 3 shown in FIG. 1B have different aspect ratios and therefore the roll radius 5 to the corners varies considerably. The radius from the Center of Mass (CoM) also varies to the various surfaces of each vehicle and is usually shorter to the top of the vehicle, represented by radius 6, than to the corners created by the sides and roof line, represented by radius 7.
The sequence of a rollover involves the vehicle moving laterally in the direction of travel, tipping towards the ground and contacting the roof rail on the near side (the first side to contact) and then contacting the second or far side roof, then the far side wheels, before continuing around to the near side wheels. The near side contact usually produces forces oriented into the near side pillars, limiting the extent of their deformation. The far side forces are typically more lateral and therefore more easily bend the pillars. Between the first near side contact at maximum radius, the flat of the roof can contact the ground. The CG falls towards the ground before being forced to rise as the far side corner with the larger radius rolls over the ground. If the roof is strong enough it does raise the CG, but if not, it collapses. The difference between the radii to the flat and the corner is a measure of the aggressivity of the structure.
Prior art rollover protection structures such as those disclosed in U.S. Pat. Nos. 3,662,177 issued to Notestine et al on Nov. 23, 1971 or 4,900,058 issued to Hobrecht on Feb. 13, 1990 which are designed for aftermarket retrofit on vehicles which may be more subject to rollover conditions such as four wheel drive vehicles, sport utility vehicles or pickup trucks employ geometric designs that require significant vertical structural elements that intrude into the cabin or usable space in the vehicle interior or must be affixed outside the normal outline of the vehicle to achieve the necessary support as disclosed in U.S. Pat. No. 7,338,112 issued to Gilliland on Mar. 4, 2008.
It is therefore desirable to maintain the rolling radius from the corner and across the flat which significantly reduces far side deformation. Additionally, it is desirable to support the roof at the major radius with a strongly cord supported bow, to transfer loads from side to side bringing the strength of pillars on both sides into play for each roof rail contact.